The present invention has broad application to the assembly of component parts wherein it is desired to enhance the bond between the parts. In addition to improved structural integrity, the present invention provides an improved hermetic seal for applications where such a seal is beneficial. Many electrical, electronic, electro-optic, fiber-optic, and photonic (hereinafter, "electro-optic") devices and circuit applications may benefit from these improved attributes and, without limitation, the present invention is described below in connection with electro-optic circuitry implemented in the communications industry.
The communication industry continues to evolve in various different aspects. One major advancement is the implementation of fiber optic technology. As is known in the art, fiber optic communications provide numerous advantages such as increased bandwidth, less noise, lower signal-to-noise ratio requirements, and lower error rates. In addition, the extremely small size of fiber optic cable relative to metallic conductors permits a much larger traffic of communication to occupy the same space previously required by metallic conductors.
As known in the art, communication through an optical fiber is accomplished by placing transmission/detection devices at the tips of both ends of the optical fiber. FIG. 1a illustrates a perspective view of certain components of such a system. Specifically, FIG. 1a illustrates a package 10 which houses the tip of the optic fiber as well as the circuitry used to transmit/receive information along the fiber. Package 10 is commonly a parallelepiped on the order of four centimeters in length and two centimeters in height. A ferrule 12 communicates with a hole or "pass through" in one side of package 10. An optic fiber 14 (illustrated in phantom) having a diameter on the order of 125 microns is aligned in an axial channel of a sleeve 16. Sleeve 16 is cylindrical in shape and has a diameter on the order of 1700 microns. The channel of sleeve 16 is typically on the order of 800 microns in diameter. Sleeve 16 and optic fiber 14 pass through ferrule 12 and into the interior of package 10. In the prior art, solder 18 or some other type of sealing material is typically used to seal the interface between sleeve 16 and the interior of ferrule 12. This seal is intended to prevent contaminants from entering the interior of package 10 between the interface of sleeve 16 and ferrule 12.
FIG. 1b illustrates a cross-sectional view of the interior of package 10 in FIG. 1a. From the perspective of FIG. 1b, note that sleeve 16 extends into the interior area 20 of package 10. Moreover, fiber 14 extends further inwardly into area 20 from a planar end 22 of sleeve 16. While not shown, it is well known in the art that the tip 24 of fiber 14 is precisely placed in a position proximate a sensing device for purposes of transmitting and receiving signals along fiber 14.
FIG. 1b further illustrates a key objective of the present invention. Specifically, as is well known in the art, it is highly desirable if not imperative that interior area 20 of package 10 be maintained hermetically sealed. Such contaminants may interfere with the delicate circuitry and its operation and, hence, may degrade system performance. Thus, various efforts have been made with respect to many aspects of package 10 and its associated componentry in an effort to ensure a minimal amount of contaminants within interior area 20. As readily apparent below, one object of the present invention is to further assure the lack of contaminants within interior area 20.
One aspect of the present invention is directed to the area where fiber 14 exits sleeve end 22. In the known embodiment of FIG. 1b, a sealing element 25 is attached to this area. Sealing element 25 is connected to sleeve end 22, thereby defining a planar interface 26 between the two pieces. Further, fiber 14 passes through sealing element 25 and into interior area 20. Unlike the loose fit between sleeve 16 and ferrule 12, however, the bond between sealing element 25, sleeve 16 and fiber 14 is heated in an effort to seal the sleeve channel which houses fiber 14 from interior area 20. In other words, without such a seal, air or other contaminants trapped within the channel of sleeve 16 could pass into interior area 20 of package 10. As described below, however, this prior art sealing technique is susceptible to failure and, hence, its function may be thwarted. In such an instance, contaminants may pass into interior area 20, thereby reducing or destroying the capability of the transmitting/receiving devices.
FIGS. 2a-c illustrate the method for constructing the seal discussed above in connection with FIG. 1b. Again, therefore, FIG. 2a illustrates a side view of sleeve 16 having an optic fiber 14 passing axially therethrough. From FIG. 2a, the flat shape of planar end 22 of sleeve 16 is better illustrated. Moreover, sealing element 25 is illustrated as a cylinder having a diameter on the order of 1000 microns, a length on the order of 1000 microns and an axial channel 28 (shown by hidden line) formed along the axis of the cylinder. Sealing element 25 in the prior art is constructed of glass.
In the prior art, and as shown in FIG. 2b, tip 24 of optic fiber 14 is threaded through axial channel 28 of sealing element 25. In addition, sealing element 25 is moved in contact with planar end 22 of sleeve 16 as shown in FIG. 2b. Sleeve 16 is then heated. Heat is transferred by conduction to sealing element 25 until it reaches or exceeds the glass softening temperature such that it begins to flow and, therefore, fuses itself to planar end 22 of sleeve 16. The resultant structure causes the bulbous shape depicted as sealing element 25 in FIG. 2c. Moreover, the flow of sealing element 25 causes it to adhere to fiber 14 as well. Thus, in the immediate instance, provided the method is properly performed, a seal is formed along planar interface 26 such that contaminants may not pass from the axial channel of sleeve 16 beyond end 22.
It has become apparent that the prior art technique discussed above suffers from various drawbacks. For example, because end 22 is planar in shape, cracks may develop along planar interface 26, thereby degrading the integrity of the seal. Naturally, if this occurs, contaminants may enter interior area 20 of package 10. In addition, the planar shape provides only a limited amount of strength in the adhesive bond between sealing element 25 and sleeve 16.
It is therefore an object of the present invention to provide a method for bonding together two different objects made of different materials.
It is a further object of the present invention to provide such a method for increasing the integrity of the hermetic seal between two objects at the time the objects are fused to one another.
It is a further object of the present invention to provide such a method for reducing the degradation of the hermetic seal between two fused objects as the fused objects age.
It is a further object of the present invention to provide such a method for reducing the degradation of the hermetic seal between two objects as the fused objects are subjected to stress, such as storage or operation of the objects under either high or low temperatures.
It is a further object of the present invention to provide such a method for bonding a fiber and sleeve wherein the bond between the two items is less susceptible to cracking.
It is a further object of the present invention to provide such a method which yields a greater compressive force at the interface between the sealing element and fiber sleeve.
It is a further object of the present invention to provide such a method wherein the integrity of the seal between the fiber and sleeve within the package interior is maintained over temperature ranges generated either under actual operating conditions, storage conditions or temperature cycling testing.
It is a further object of the present invention to provide such a method which substantially decreases the possibility of contaminating the interior area of a fiber optic circuit package.
It is a further object of the present invention to provide such a method which substantially enhances the longevity and operability of a fiber optic circuit package.
Still other objects and advantages of the present invention will become apparent to those of ordinary skill in the art having references to the following specification together with its drawings.